It’s been a busy week for Angry Birds developer Rovio Mobile. It’s releasing updates to many of its mobile apps, it just dropped a new branded browser game, and it stared down a multi-billion-dollar offer from gaming giant Zynga.

In the iTunes App Store, Angry Birds is looking toward the winter holidays. The developer just cranked out another 25 themed levels in a new update for Angry Birds Seasons called “Wreck the Halls” (I love that), which is free for players of the title, available in both free and $0.99 versions. Seasons updates are pretty regular (hence the title of the app), but with 350 million downloads of the game across all platforms, throwing out 25 new levels creates a pretty big splash.

That many customers, both paying for Angry Birds and consuming ads in its free version, probably accounts for why Rovio Mobile reportedly turned down a $2.25 billion bid from the FarmVille-making Zynga to acquire the company. According to a story from the New York Times, Zynga was in talks to acquire Rovio earlier this year – it has snapped up something like 14 gaming companies in the last year, at a major expense to its profit margin in 2011 – but Rovio walked away. Somehow, $2.25 billion feels like a low bid for the entire Angry Birds juggernaut.

And while Angry Birds’ biggest share of the market is still on Apple’s iOS mobile platform, according to Ask Your Target Market, it isn’t nearly Rovio’s only target. The company is actively pursuing other partnerships and other platforms, it seems. For one, just as Seasons got an update for the holidays, the app version for Google’s Chrome web browser has also received another 25 levels. If you run the battery out in your iPhone, you can always crank up a computer and keep playing.

In terms of other partnerships, Rovio has created a branded Angry Birds title as part of an advertising venture with Wonderful Pistachios, as Pocket Gamer reports. It’s a browser-based version of Angry Birds with five levels, two of which are available for free and the other three accessible using codes garnered from packages of the aforementioned pistachios. It’s not the first time Rovio has paired with another company to make a branded Angry Birds title. It did the same with the high-quality Angry Birds Rio, a version that included characters from Fox’s Rio animated film.

Rovio Mobile hasn’t been exactly struggling since Angry Birds was released in 2009, but its killer franchise seems to continue to grow and overtake more and more media. There are rumblings of cartoons and maybe a film on the horizon, plus simply a ton of Angry Birds games on all sorts of platforms, ranging from PC web browsers to PlayStation 3s. It seems smart that Rovio hasn’t sold the company – there’s a whole lot more money to be made.